# The relationship between variables and controls in an experiment

### Variables in Your Science Fair Project

The factors that can change value during an experiment or between of Control, Constant, Independent and Dependent Variables in a Science The point of an experiment is to help the experimenter define the relationship. Variables: Independent, Dependent and Controlled. Back to page one conducting experiments, one needs to deal with variables, those factors or elements. Cause and effect relationships explain why things happen and allow you to An experiment usually has three kinds of variables: independent, dependent, and Controlled variables are quantities that a scientist wants to remain constant, and .

For example, to test the hypothesis that a seed needs light to germinate, the independent variable would be whether the seed was left exposed to light or covered with soil. If you hypothesize that Cub Scout pinewood derby cars are faster when the weight is near the rear, the placement of the weight is the independent variable.

Dependent Variable The dependent variable is what is measured or observed. It is the "effect" in the cause-and-effect relationship.

In the seed experiment, seed germination would be the dependent variable. For the pinewood derby car, the time it takes the car to go down the ramp is the measurable, dependent variable. Each time you change the independent variable, such as by placing the car weight different distances from the rear, take a measurement. Sciencing Video Vault Controlled Variable In order for the test to be fair, other factors that could affect the outcome of the experiment should be kept the same, or controlled.

For the seed experiment, seeds should come from the same species, source and storage conditions. The temperature, watering, planting mix and exposure period should be the same. In the pinewood derby experiment, controlled variables might include the car design; the height, length and smoothness of the ramp; initial placement of the car on the ramp; and the kind of metal in the weight.

Sometimes controlled variables are called "constant variables. Confirming Variable Identification The National Center for Education Statistics suggests the following test to identify independent and dependent variables correctly.

### Control variable - Wikipedia

Put the appropriate words for your experiment in this sentence to see if they make sense: Independent variable causes a change in dependent variable and it isn't possible that dependent variable could cause a change in independent variable.

For the seed experiment, the test sentence would read: In other words, scientists design an experiment so that they can observe or measure if changes to one thing cause something else to vary in a repeatable way. The things that are changing in an experiment are called variables.

A variable is any factor, trait, or condition that can exist in differing amounts or types. An experiment usually has three kinds of variables: The independent variable is the one that is changed by the scientist.

Well, if you changed more than one variable it would be hard to figure out which change is causing what you observe. For example, what if our scientific question was: The data might get a bit confusing— did the larger dog eat less food than the smaller dog because of his size or because it was the middle of the day and dogs prefer to eat more in the morning?

## Control variable

Sometimes it is impossible to just change one variable, and in those cases, scientists rely on more-complicated mathematical analysis and additional experiments to try to figure out what is going on. Older students are invited to read more about that in our Experimental Design for Advanced Science Projects page.

To be clear though, for a science fair, it is usually wise to have only one independent variable at a time. If you are new to doing science projects and want to know the effect of changing multiple variables, do multiple tests where you focus on one independent variable at a time. The dependent variables are the things that the scientist focuses his or her observations on to see how they respond to the change made to the independent variable.

In our dog example, the dependent variable is how much the dogs eat. This is what we are observing and measuring. It is called the "dependent" variable because we are trying to figure out whether its value depends on the value of the independent variable.

If there is a direct link between the two types of variables independent and dependent then you may be uncovering a cause and effect relationship. The number of dependent variables in an experiment varies, but there can be more than one.

INTERACTIVE: Part 1: Identify the Independent and Dependent Variables with the MythBusters!